There are many different types of polymerization catalysts which are used to produce olefin (co) polymers. The use of different catalysts allows the production of polymer products which have different physical properties.
It is often desirable to switch between different polymerization catalysts in order to respond to market demands for different polymers. However, it is not a trivial undertaking to transition between some catalysts because different catalysts are often incompatible with one another—for example, it is well known that an active Zeigler Natta catalyst may “poison” an active metallocene catalyst (i.e. severely reduce the activity of the metallocene catalyst).
Accordingly, many attempts have been made to develop technologies which facilitate catalyst transitions, including these technologies disclosed in United States Patent U.S. Pat. No. 6,949,612 (Agapiou et al.); U.S. Pat. No. 6,284,849 (Almquist et al.); and U.S. Pat. No. 6,897,269 (Schreck et al.).
In general, these prior processes require that the first polymerization catalyst be “killed” or substantially deactivated. Although these technologies do mitigate problems resulting from undesirable reactions between two incompatible catalysts, these technologies may introduce other problems such as:
(i) the need to carefully control the addition of the deactivator agent (so that it does not become a poison for the new catalyst); and
(ii) the need to allow downtime for the deactivation reaction (and generally, the subsequent purging of the deactivator).
This second problem—i.e. “downtime” can cause further problems, particularly if it requires that polymer finishing operations (such as polymer degassing and pelletizing operations) be stopped and restarted. For example, the seals and/or bearings or mechanical pumps and compressors which are used in the polymer finishing operations may be more likely to fail during a shut down/start-up cycle than they would otherwise be during continuous operation.